Abnormality diagnosis apparatuses for an internal combustion engine system which starts operation by supplying cylinders with compressed air stored in an accumulator have been proposed. An abnormality diagnosis apparatus for an internal combustion engine system confirms whether inside of the accumulator is decompressed or pressurized, on the basis of an output signal from a pressure sensor which outputs a signal corresponding to the pressure in the accumulator. If it is confirmed that the pressure in the accumulator is decreasing, it is confirmed whether the decompression rate is faster than a standard decompression rate that accompanies starting of an internal combustion engine. If the decompression rate is faster than the standard decompression rate, it means that a great amount of compressed air is consumed during starting, and thus it is diagnosed that abnormality such as air leakage exists in a compressed-air supply system of the internal combustion engine. If compression inside the accumulator is confirmed, it is confirmed whether the compression rate is slower than a standard compression rate that accompanies accumulation of pressure in the accumulator. If the compression rate is lower than the standard compression rate, it means that abnormality exists in a compressor, and thus it is diagnosed that abnormality exists, such as malfunction of the compressor or air leakage in a compressed-air supply system of the internal combustion engine (see Patent Document 1, for instance).